Oxygen metabolism, oxidative stress and acid-base physiology of dental plaque biofilms

Abstract

Dental plaque is a natural biofilm which has been a focus of attention for many years because of its known roles in caries and periodontal diseases. Acid production by plaque bacteria leads to the erosion of tooth mineral in caries, and the cariogenicity of plaque is related to population levels of acid-tolerant organisms such as mutans streptococci. However, the biofilm character of plaque allows for survival of a diverse flora, including less acid-tolerant organisms, some of which can produce ammonia from arginine or urea to counter acidification. Plaque is often considered to be relatively anaerobic. However, evidence is presented here that both supragingival and subgingival plaque have active oxygen metabolism and that plaque bacteria, including anaerobes, have developed defenses against oxidative stress. Even in subgingival plaque associated with periodontitis, measured residual oxygen levels are sufficient to allow for oxygen metabolism by organisms considered to be extremely anaerobic such as Treponema denticola, which metabolizes oxygen by means of NADH oxidases and produces the protective enzymes superoxide dismutase and NADH peroxidase. The finding that plaque bacteria produce a variety of protective enzymes is a good indicator that oxidative stress is a part of their everyday life. The biofilm character of plaque allows for population diversity and coexistence of aerobes, anaerobes and microaerophiles. Overall, agents that affect oxidative metabolism offer possibilities for reducing the pathogenic activities of plaque.

Dental Caries: A Microbiological Approach

“…Phenotypic adaptation and stress response mechanisms such as tolerance of acid, starvation, oxygen, fluoride and expression of urease [44,[46][47][48][49]52,[54][55][56][57]. that are common among strains of a species can be regarded as support of bacteria to survive stresses common to their habitats due to 'stress proteins' [58][59][60][61].…”

Virulence modulation of Streptococcus mutans biofilms by metal ions released from orthodontic appliances

“…However, because S mutans lacks catalase with which to detoxify reactive oxygen species (ROS), it is also possible that trivalent ions were reduced to Fe 2+ and Cr 2+ as a result of the acidity of the biofilm and the low availability of molecular oxygen. 21 Once internalized by the bacterial cells, these reduced ions might have begun to catalyze the Fenton reaction, with subsequent production of hydroxyl radicals, which are strong oxidizing agents that affect cellular functions. At the level of microbial populations, the presence of ROS would have killed cells of outer layers of biofilm, as well as internal layer cells, to a lesser extent, resulting in lower biomass after 12 hours of treatment.…”

Responses of Cariogenic Streptococci to Environmental Stresses

“…As would be expected, oral bacteria do possess multiple, and often overlapping, pathways for dealing with oxidative stresses in the cell and environment (Marquis, 1995;Mongkolsuk and Helmann, 2002). The levels of respiratory/oxidative stress enzymes reflect the respiratory capacity of the organism.…”

“…Although oxidative stress has relevance in plaque ecology (Marquis, 1995), few detailed studies of the molecular mechanisms regulating oxidative stress responses in oral bacteria are available. Yet, these organisms are constantly exposed to oxidative agents from either intracellular or extracellular origin.…”